In optical communications, light is modulated at a transmitter end of an optical fiber, transmitted to a receiver end of the optical fiber, and detected at the receiver end, where it is demodulated to retrieve the information being communicated. Typically, semiconductor laser diodes are used to generate the information-carrying light, and semiconductor photodiodes are used to detect the transmitted light at the receiver end.
Reliability and environmental requirements for telecommunications equipment, including optical communications equipment, are known to be quite stringent. It is common for telecommunication equipment components, even for those usable in a “central office” environment, to be constructed to withstand, without failure, hundreds and even thousands of hours of operation at extremely challenging environmental conditions, such as 85° C. at 85% of relative humidity. These stringent environmental requirements are usually met by using a hermetically sealed package enclosing the components.
Although reliable, hermetic packages are costly to produce and to seal. The cost of hermetic packages can be comparable to the cost of the semiconductor devices, such as lasers or photodiodes, sealed within the packages. In modern business environment, a motivation exists to reduce costs of telecommunications equipment. The cost reduction could in principle be achieved by providing semiconductor devices that are tolerant to high temperature, high humidity environment, so that no hermetic packages are required to protect them.
Unfortunately, it is rather difficult to make semiconductor devices humidity tolerant. Semiconductor devices contain thin film layer stacks. Water molecules are known to attack the integrity of the stacks at elevated temperatures, causing layer delamination and a device failure.
In US Patent Application Publication 2006/0076589 A1 incorporated herein by reference, Gao et al. disclose a PIN photodiode and a method of manufacturing a PIN photodiode that has reduced delamination of dielectric layers. Referring to FIG. 1, a PIN photodiode 100 of Gao et al. has a semi-insulating (SI) substrate 101, a second type electrode 102 disposed on the substrate 101, an intrinsic layer 104 disposed on the second type electrode 102, having a horizontal step 105 between portions 104a and 104b, a first type electrode 106 disposed on the intrinsic layer 104, and a first electrode contact metal 107. A first electrode bonding pad 111 is coupled to the first type electrode 106 through a via 109. The stack of layers 102 to 106 is covered with a dielectric layer 108 sealing the structure 102/104/106. The horizontal step 105 in the intrinsic layer 104 of the PIN structure is for improving adhesion of the dielectric layer 108 and for confining the extent of delamination of the dielectric layer 108. Detrimentally, the delamination of the sealing dielectric layer 108, although localized due to the presence of horizontal step 105, may still be present in the device 100 of FIG. 1.
In US Patent Application Publication 2008/0283975 A1 incorporated herein by reference, Matz et al. teach that a thin silicon oxide layer improves adhesion between an etch stop layer and an ultra-low k dielectric layer of a semiconductor device. Detrimentally, the improved adhesion of the etch stop layer does not reduce or prevent delamination of a sealing layer in a high humidity environment.
The prior art lacks a semiconductor device and a method for manufacturing a semiconductor device, in which delamination of the entire sealing layer in a high temperature, high humidity environment were reduced. Accordingly, it is a goal of the present invention to provide a device having reduced delamination of layers, and a method of manufacturing such a device.